QOTD: “I’ll never underestimate the power of cat urine”

A customer came into the shop yesterday with a Mavic Ksyrium SL front wheel. It’s a second generation, circa 2002-2005, the black one that first had the machining in between the spokes. It’s in excellent shape, except for the broken spoke. In my memory, the first generation production of the Ksyirums had spoke failures a little too frequently for my tastes, but Mavic seemed to have largely overcome that in the later models. Even so, there is nothing terribly surprising about a decade old wheel popping a spoke.

Then the customer explained that when he and his wife were moving to a new place in town about 8-9 years before, they had temporarily stored a bunch of stuff at his mother’s property, including his titanium Davidson bike. At the end of winter when he came to retrieve all the things for the new place, the front wheel was thoroughly encrusted with “yellow crystals”. Apparently, there was a resident cat that for whatever reason decided that the Davidson bike, specifically that wheel on the bike, was going to be its personal toilet all winter long. The customer wondered if that had weakened the metal of the spokes.

I paused for a moment, furrowed my brow as I spun up my random access memory to recall my old engineering classes. That was a long time ago, and that fall semester I was working nights and splitting my weekends between bike racing financed by nights of delivering pizza and raves fueled by a lot of drugs. I pictured myself in the classroom in the New Engineering Building and the transparencies projected onto the screen at the front of the class. Then I said, “I don’t remember the exact behaviours of corrosion fatigue for aluminium alloys, but it is possible that something in cat pee might accelerate pitting or intergranular corrosion, leading to faster crack initiation which ultimately reduced the service life of the spoke once cyclical loads were reapplied during riding usage…but I just don’t remember if aluminium is vulnerable to concentrated ammonia.”

To which the customer said, “I will never underestimate the power of cat urine.”